Recorder-reproducer



D. J. MUNROE l I l l I Ill Ill W om WN Sept. 7, 1954 Orl inal Filed MarSept 7, 1954 D. J. MUNROE RECORDER-REPRODUCER 2 Sheets-Sheet 2 OriginalFiled March 4, 1949 Zinn/'ve Patented Sept. 7, 1954 UNIRECORDER-REPRODUCER David J. Munroe, Racine, Wis., assignor to WebsterElectric Company, Racine, Wis., a corporation of Delaware Originalapplication March 4, 1949, Serial No. 79,663. Divided and thisapplication June 14, 1951, Serial No. 231,502

1 claim. 1

' The present invention relates to magnetic recorder-reproducerapparatus and has for its primary object the provision of a new andimproved method of and apparatus for erasing the previous history ofrecording from a magnetic record medium and thus preparing orconditioning it for a new record. The present application is a divisionof my copending application Serial No. 79,663, filed March 4, 1949.

Despite long continued and persistent efforts, no one, prior toi thepresent invention, Was able to provide a method of or apparatus fullysatisfactory to erase previous records from magnetic record media,especially the so-called "high flux tapes. According to the presentinvention, this is accomplished by `a novel method including the stepsof magnetically saturating the tape, decreasing the magnetization, andthen subjecting the tape to a high frequency alternating currentmagnetic eld substantially to demagnetize it. It has been found thatthis method is eminently satisfactory to erase previous records fromdifferent types of tapes, including the high flux tapes. Also, theapparatus is quite simple, including only a. permanent magnet and analternating current erasing means, the two being located in spacedrelation along the path of movement of the tape.

Other objects and advantages of the present invention will becomeapparent from the ensuing description of an illustrative embodiment ofthe invention, in the course of which reference will be had to theaccompanying drawings, in which:

Fig. 1 is a fragmentary top plan view, partly broken away, ofrecorder-reproducer constructed in accordance with the presentinvention;

Fig. 2 is an enlarged fragmentary top elevational vieW of a portion ofthe apparatus shown in Fig. 1 and illustrating details of the tapeco-nditioning means;

Fig. 3 is a graph used in explanation of the tape conditioning method;and

Fig. 4 is a schematic Wiring diagram of the apparatus as a Whole.

Referring first to Fig. 1 the apparatus is illustrated in its stopposition with certain covering structure partly broken away and Withoutits accompanying cabinet and front plate. As heretofore indicated thepresent application is a division of my above referred to copendingapplication and only sufficient of the apparatus is herein illustratedand described to enable those skilled in the art to ascertain the natureand advantages of the invention. The invention may be utilized withvarious types of medium but it is particularly designed for use with anelongated magnetizable record medium such as tape coated or impregnatedwith magnetic material.

The recorder-reproducer is indicated as a Whole by reference characterl0. It includes a suitable cabinet I2 having a top panel or base plateI4 and it may be provided with a front panel and top covers that are notshown.

The apparatus illustrated is provided with control means forconditioning the .apparatus for recording, reproducing, rewinding andfast for- Ward speed. The control means illustrated includes a knob 20adapted readily to be graspable by the operator and rotated into variouspositions. The knob is located near the center and at the front of thebase plate so that its position can be readily noted and so that it canbe easily operated. In order readily to indicate the position of theknob, it is provided with an enlarged lower skirt-like portion 22 uponwhich is formed an arrow-like point 24, cooperating with suitableindicia printed or otherwise suitably formed on the base plate toindicate the positions referred to above. As indicated, the apparatus isillustrated in its stop position.

The apparatus may include means for preventing accidental conditioningof the apparatus for recording, during which tape conditioning meansincluding the erase means is effective. This preventing means mayinclude an interlock mechanism, not shown in full, but comprising a pushbutton 26 extending above the base plate and which can be depressed topermit control knob 20 to be moved to its record position.

The apparatus can be conditioned for fast forward speed upon movement ofa control lever 28 from its indicated solid line position to the phantomline position. This movement can be effected only when the knob 20 is inits listen position.

The reco-rd medium is supported above the base plate, and preferably butnot necessarily in transparent reels mounted above a suitably markedportion of the base plate so as to enable the operator of the recordreadily and immediately to observe the length of tape upon both thesupply and take-up reels, the length preferably being indicated by theplaying or recording time time in minutes. This feature is furtherdisclosed and claimed in my copending application, Serial No. 206,867filed January 19, 1951 Referring again more particularly to Fig. l,

the supply reel is indicated by the reference character 30 and thetake-up real by the reference character 32. The two reels may beidentical in construction Aand may be made of some suitable transparentplastic material, such as Lucite. In Fig. l, the record medium,indicated by reference character 34,. is shown partly upon the supplyreel and partly upon the take-up reel. The reels may be of suitablesize, those illustrated being adapted to hold about 1,250 feet of recordmedium and may be and is shown as being coated paper. The base plate isprovided with suitable scales 36 and 38 at locations immediately beneaththe reels, whereby the length of tape upon each reel can be ascertainedat a glance. The scales are identical and include time markings runningabout thirty minutes. The main graduations are subdivided in suitablemanner to enable the operator easily to determine the playing time inminutes.

The tape is driven in forward drive by means including a continuouslyrotating mechanical capstan 40 rotated at constant speed by a motor(shown schematically by reference character |88 in Fig. 4) and anassociated rubber tired pinch roller 42 adapted to hold the tape againstthe capstan so that the tape will be properly driven thereby. The pinchroller is mounted at the end of a lever 44 and is selectively movable tomove the roller into and out of engagement with the capstan. The tape isguided by a guide roller 48 located some distance from the capstan.Between the capstan and guide roller is located a transducer 50including a core 5| and which is utilized both in recording orreproducing and against which the tape is held by a selectively movablepressure pad 52. Also located between the capstan and pinch roller isthe tape conditioning or erase means 54 of the present inventioncomprising a permanent magnet 56 and an alternating current erasingmeans including a transformer 58 and which is adapted selectively to bemoved into and out of cooperative engagement with the tape, it beingshown out of cooperative engagement with the tape, as it is in the stopposition, but being movable to bring the permanent magnet andalternating current erase means into cooperative engagement with thetape in the record position.

The tape conditioning means 54 of the present invention, as indicated,includes two tape conditioning devices. The rst of these, irst in thatit acts upon the unconditioned tape before the other, is a generallycircular permanent magnet 56 mounted within a plastic cover 60 andsupported upon an erase head lever 62 extending above the top of thebase plate through an aperture 64 in the plate. The second of theconditioning means is an alternating current erasing means including thetransformer 58 and also mounted upon the lever 62. The transformerincludes (see also Fig. 4) a primary winding 66 and a single turnsecondary winding 68 of which the former is supplied with a highfrequency alternating current, as will be described in greater detailhereinafter. The lever 62 is movable be.- tween what may be termedoperative and inoperative positions. In the operative position, intowhich it is moved only in the record position of the control knob 20,the erasing means 54 is moved into cooperative relationship to againstthe tape 34.

The recording and reproducing head 50 and the erasing means 54, as Wellas the pressure pad assembly, are normally enclosed by the covers 4 and12. Ihey are detachably secured to the base plate as by the screws 14.

The electrical circuits and controls of the recorder are illustrated inFig. 4 to which reference will now be had, The control means includes aswitch assembly operable by the control knob 20 which also operates theindex plate. The selector switch is operable into four positions, therecord, listen (also fast forward), stop, and rewind positions. Therecorder includes separate recording and reproducing or playbackchannels, the latter of which is also utilized as a means for monitoringthe recording.

Referring now to Fig. 4, it will be noted that the switch assembly 80 isillustrated in its record position. In this position the record coil 82of the record-playback head 50 is supplied with the signal to berecorded and also with a high frequency constant amplitude signal froman oscillator 84, which may be of the Hartley type and have two outputcoils 86 and 88, the former of which supplies a high frequency currentto the record head and the latter to the primary winding 65 of the erasetransformer 58. The record coil 82 is also supplied with the inputsignal through an amplifier section 90, which is common to both recordand playback channels 92 and 94. The amplifier is connected to therecord channel through a record volume control 96. The latter isconnected to an amplier section 98, to the output of which is connecteda record indicator |00. rI'he output of the amplifier 98` is connectedto transformer |02 and the secondary winding |04 of the latter isconnected in series with the record coil 82 and the oscillator outputcoil 86. This series connection is effected through conductor |06,switch blade |08, conductor H0, the record coil 82, conductor H2, switchblade ||4, the shield conductor H6, conductor I8 (which is grounded at|20), the output coil 8S, and conductor |22.

The alternating current erase means transformer primary winding 56 isconnected to the oscillator output coil 88 permanently through a circuitincluding conductors |24 and |26, the latter of which may be connected,as shown, to the frame of motor |88, which is grounded.

The oscillator is rendered operative only in the record position of theswitch 80. In this position the plate circuit of the oscillator iscompleted through conductor |28, switch blade |30, and the plate voltagesupply conductor |32 leading to a lter |34 connected to the output of arectifier |36, which may be of conventional construction.

Brief consideration will now be given to the remainder of the circuit ofFig. 4. In the record position the input of amplifier 90 is alsoconnected to both the high and low level jacks |30 and |32. Thisconnection includes a grounded conductor |34, conductor |36, switchblade |38 and conductor |40.

The playback channel 94, which is also used for monitoring duringrecording, is connected to the output of the amplifier 80 through alistening volume control |42. The latter is connected to an ampliersection |44. Bass and treble controls |46 and |48 are connected to theoutput of amplifier |44. The channel includes also a tube |50 of thedual triode type, an inverter-amplier section |52, a push-pull outputstage |54, to the output of which are connected a loud speaker |56 andan external speaker jack |58.

, In use the recording volume is controlled through the use of therecord indicator.

bass and treble controls are independent of the record control so thatadjustment of them to provide a good loud speaker output does not affectthe recording.

In the listen position of the switch 3d, the oscillator 3d is renderedinoperative, the record coil 32 is disconnected and the playback orreproduce coil. Se@ is connected to the input of amplifier 9d, whichremains connected to the playback Channel Sil and thus to the loudspeaker, The reproducer coil is connected to the amplier input throughthe shielded conductors lZ, ld, the switch blades 166 and H58,conductors il@ and H2, switch blades IBS and VM, and conductors 36 andi3d, respectively.

In the stop position of the switch, both the record and playback coilsare disconnected, the oscillator remains inoperative, and the amplierinput is connected to the input jack.

In the rewind position the record coil is disconnected, the oscillatoris inoperative, and the playback coil IG is connected to the input ofthe amplifier.

Power may be supplied to the recorder from the usual 110 volt powersupply lines through a plug |76. One of the plug conductors |18 isconnected through a fuse i8!) to the primary winding 82 of the powertransformer associated with rectier E36. The other conductor i845 isadapted to be connected to the other terminal of the primary windingupon closure of an onoff switch 86. The apparatus is provided with thepreviously mentioned constant speed motor 83 driving the capstan andtape spools and which is adapted to be energized upon the closure of amotor switch E99.

The erasing means of the present invention is thus rendered electricallyeiective by switching means and is mechanically shifted against the tapein the record position of the control knob. Accordingly both thepermanent magnet and the alternating current erasing means act upon thetape and they, conjointly, provide a very eiective tape conditioningmeans and one Which is particularly suited for high ux tapes-i. e.,tapes which have high retentivity. The method also enables a relativelysmall alternating current erasing means to be used and requires butlittle power.

The tape conditioning method of the present invention comprises thesteps of saturating the tape, decreasing the magnetization and thensubjecting the tape to a high :frequency alternating current magneticeld substantially to demagnetize it. The saturation land decrease insatu- I ration are accomplished by moving the tape past a direct currentmagnet having a core with a narrow air gap providing a region of highintensity magnetization and pole pieces which recede from the path oftape movement. This can be conveniently done through the use of a magnetcore that is substantially circular at its external periphery, such asthe core 5l. The tape passing past the magnet is magnetized sufficientlysubstantially to saturate it when it is in the region of the gap, asindicated by the point P on the graph of Fig. 3. At this point themagnetic coating of the tape is subjected to a magnetizing force l-lmsxproducing iiux of an intensity Bmx. If the tape could be moved out ofthis eld with no further inuence from the magnet, the magnetic materialwould reta-in a peak residual magnetism represented by Br. The tape,however, is gradually moved away from the gap and, at the same time, itmoves away from the core. In so doing it is subjected to a demagnetizingforce, which can be assumed to be Ha so that the coating on the tape isdemagnetized to have a residual magnetism Bw as it leaves the permanentmagnet. The reduction is such that when the alternating current magneticfield acts on the tape, substantially all of the remaining previousmagnetization is removed.

The foregoing tape conditioning method has been found very effectivewith high iiux tapes, which cannot be satisfactorily conditioned bydirect current or alternating current erasing methods. Also, alternatingcurrent erasing apparatus requiring less power can be used.

While the present invention has been described with an illustrativeembodiment, it should be understood that the details thereof are notintended to be limitative of the invention except insofar as set forthin the accompanying claim.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

Magnetic recording apparatus, including in combination, magneticrecording means for recording upon a movable elongated magneticrecording medium and apparatus located in advance of said recordingmeans for conditioning the moving magnetic medium for recording by saidmeans, said conditioning means including a permanent magnet located inproximity to the moving recording medium and adapted magneti-vReferences cited in the nie of this patent FOREIGN PATENTS Country DateFrance Mar. 15, 1943 Number

